Split Link Adaptation for Unlicensed Spectrum Throughput
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Solution Overview
Problem
In wireless communication networks, especially in unlicensed spectra like 2 and 5 GHz, interference from mixed technologies such as WiFi and LTE-U leads to inefficient channel usage and increased error rates due to the lack of Listen-Before-Talk (LBT) functionality, causing collisions and reduced throughput.
Innovation Solution
A network node employing split Link Adaptation (LA) and varying Modulation and Coding Schemes (MCS) across subframes of a transmission burst, with a more aggressive MCS used in less interfered subframes to improve data reception and reduce overhead, allowing for efficient channel usage and faster user completion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single MCS is used for all subframes in a transmission burst, then the system complexity is reduced and implementation is simpler, but the throughput is reduced due to inefficient channel usage in less interfered subframes
Solution Approach 1:
The transmission burst is divided into multiple subframes, each potentially using different MCS indices. The network node determines separate MCS indices for different subframes based on channel conditions, allowing optimized transmission for each subframe while maintaining overall system manageability through structured segmentation.
Solution Approach 2:
The MCS index is made dynamic across subframes rather than static for the entire burst. The network node can adjust the MCS index for each subframe based on real-time channel conditions and interference levels, enabling adaptive optimization of throughput while managing complexity through systematic dynamic adjustment.
2Speed
If LBT is not used in unlicensed spectrum, then the channel access is faster and simpler, but collisions with other technologies like WiFi increase causing interference and reduced reliability
Solution Approach 1:
Instead of implementing full LBT which would significantly slow down channel access, the system uses a simplified approach with partial sensing or reduced LBT categories. This allows faster channel access while providing some level of collision avoidance, balancing speed and reliability without the full overhead of traditional LBT.
Solution Approach 2:
The system changes key parameters of the LBT mechanism, such as reducing the sensing window duration, adjusting energy detection thresholds, or modifying backoff parameters. These parameter adjustments enable faster channel access while maintaining adequate collision avoidance, optimizing the balance between speed and reliability for unlicensed spectrum operations.
3Productivity
If a conservative MCS is used for all subframes to ensure reliable reception, then the transmission reliability is improved, but the throughput is reduced due to insufficient exploitation of less interfered subframes
Solution Approach 1:
Different MCS indices are applied to different subframes based on their specific channel conditions. Subframes with better channel quality can use higher MCS indices for improved throughput, while subframes with poorer conditions use lower MCS indices to maintain reliability. This local optimization approach maximizes overall throughput while ensuring adequate reception reliability for each subframe.
4Adaptability or versatility
If the network node transmits in duty cycles with long silent phases to evaluate carrier load, then the channel usage adaptation is improved, but the productivity is reduced due to extended transmission delays
Solution Approach 1:
The system uses periodic carrier sensing and evaluation at defined intervals rather than continuous monitoring. Transmission bursts are structured with periodic silent phases for carrier evaluation, allowing the network node to adapt to channel conditions periodically while maintaining high data transmission rates during active phases. This periodic approach balances adaptability with productivity by minimizing the time spent in silent evaluation phases.
Data Source
AI summary
A network node and a method performed by the network node for performing a transmission to one or more wireless devices are provided. The network node is operable in a first communication network, supports carrier aggregation, and provides a PCell in a licensed frequency band and a SCell in an unlicensed frequency band. The method comprises determining to employ splinted Link Adaptation (LA) for a downlink transmission on the SCell; and employing a first Modulation and Coding Scheme (MCS) on one or more first subframes of a transmission burst to be transmitted to the one or more wireless device and at least a second MCS on one or more subsequent subframes of the transmission burst to be transmitted to the wireless device.